Any one use these? Any good?

http://www.e-ztower.com/

I'm curious how high I can prop up my blind with these and remain safe. I can buy 14 foot 4X4s.

Can't speak to those but I use these.

http://www.basspro.com/Elevator-Bracket-Set/product/82431/

They are based on weight  but I have a 5x8 platform with walls and a 6 foot high tin roof. It's about 6 ft off the ground but as long as you stay under
1000 lbs and brace the crap out of it, you should be good.

I've used the elevators brand.  They worked well, and have stood up to use without problems.  My blind is 5x7, with a 2x6 and 3/4" ply floor, 7 foot walls, and a galvanized metal roof over 2x4's.  Its not  light blind!  And I've had myself (250#) and a buddy, closer to 3253 in it.  Again not issues.  And we are using 14 foot 4x4 with diagonal bracing....

I do get  lot of wind.  I didnt want my blind blowing over, so I drove 2x2" x4' angle iron in to the ground by the legs and lagged the legs to the angles, then used earth anchors and rope to provide lateral bracing against wind.  We had a microburst that dropped all kinds of trees and blew the roof off a barn not 200 yards away.  No issues with the blind or the legs.

+1 for elevators